The present invention relates to a gas turbine, particularly a scroll-type gas turbine, driven by exhaust gas from an internal combustion engine and, more particularly, to an improvement in the nozzle portion of the gas turbine of the type mentioned above.
A scroll-type gas turbine driven by the exhaust gas from an internal combustion engine is disclosed in Japanese Unexamined Patent Publication No.. 166718/1985, for example. This gas turbine has a scroll casing into which the exhaust gas from the engine is introduced. The exhaust gas introduced in the space or scroll chamber of the scroll casing flows in the form of a spiral or vortex flow which is directed from the outer peripheral portion towards the inner peripheral portion of the chamber defined by the scroll casing. The gas turbine also has an impeller which is rotatably mounted in the central portion of the scroll casing and adapted to be rotationally driven by the energy of the exhaust gas from the scroll chamber. The exhaust gas after the work is discharged by the impeller in the direction of the rotation axis of the impeller from the central region of the impeller.
A nozzle structure is provided at the inner peripheral edge of the scroll casing so as to surround the impeller. A plurality of guide vanes are arranged and oriented in the orifice or aperture of structure such that the exhaust gas from the scroll casing can be deflected and directed towards the impeller therethrough.
The guide vanes are attached at their respective one ends to the inner surface of one of the opposing walls of the scroll casing forming the nozzle structure and extend such that the other ends thereof are located in the vicinity of the inner surface of the other of the opposing walls of the scroll casing.
This known scroll-type gas turbine suffered from the following disadvantage owing to the distortion of the guide vanes due to thermal stress. More specifically, during operation of the gas turbine, the guide vanes were distorted or deformed in the circumferential direction due to heat so that the size of the gap between the ends of the guide vanes and the inner wall surface of the scroll casing opposed or faced thereto was increased. In consequence, the proportion of the gas passing through the above-mentioned gap to the total gas passing through the orifice or aperture in the nozzle was increased with the result that a proportion of the enthalpy of the gas converted at the nozzle into kinetic energy effective to drive the impeller was decreased, which led to the decrease in the total efficiency of the gas turbine.